The present disclosure relates to a method for determining distances and, in particular, ride heights in order to measure a chassis of a motor vehicle, and a chassis measuring device for carrying out the method according to the disclosure.
Contactless axle measurement such as is known, for example, from DE 10 2004 013 441, is based on the detection of a geometry detail of a wheel rim, the evaluation with respect to the position in space and the combination of the results to form an axle measurement.
In addition to the pure measured values, which describe the position of the wheel rims with respect to one another, the vehicle-specific predefined values, for example the structural position or an admissible range of the ride height which is predefined by the vehicle manufacturer, are necessary for an evaluation, which comprises, for example, a setpoint value/actual value comparison. The ride height is defined differently here by different vehicle manufacturers. According to one definition the ride height is defined as a difference in height between the upper edge of the wheelhouse and the upper edge of the rim. Other definitions consider, for example, the level at an element of the wheel suspension or the difference in height between the contact patch and a body feature.
Different load states of a vehicle result in different ride heights and therefore also different spring compression travel values for the same type of vehicle. Different spring compression travel values produce different results of the chassis measurement, for example, different toe—in values and camber values.
The ride height of a vehicle is conventionally measured using mechanical aids by measuring distances between fixed points on the vehicle and the contact patch, recording the measured values manually and inputting them into a computer of the chassis measuring device. Alternatively, the distances are measured with a special tool and transmitted to the computer via an interface.
This is laborious, tedious and susceptible to faults. In addition, accurate measurement is made more difficult by the fact that direct mechanical contact with the feature points to be measured is frequently impossible or can only be achieved with difficulty.
WO 2008/028832 A1 describes a method for determining distances for measuring a chassis in which firstly in each case an image of a wheel rim and an image of at least one area adjacent to the wheel rim are recorded by means of at least two measuring cameras of a measuring device. At least a first spatial point is then determined in the two recorded images of a wheel rim and the position of said first spatial point is calculated by means of triangulation. Subsequently, at least one second spatial point is determined in the two recorded images and the position of said second spatial point is calculated by triangulation. After this, the distance or the difference in height between the two spatial points is determined. The ride height of the vehicle can be determined directly or indirectly from the distance or the difference in height without the help of mechanical aids.